1. Field of the Invention
The present invention relates to methods for making liquid crystal display screens and, particularly, to a method for making a carbon-nanotube-based liquid crystal display screen.
2. Discussion of Related Art
Referring to FIG. 1, a conventional liquid crystal display screen 100 for liquid crystal display (LCD), according to the prior art, generally includes a first substrate 104, a second substrate 112, and a liquid crystal layer 118. The first substrate 104 is disposed opposite to the second substrate 112. The liquid crystal layer 118 is located between the first substrate 104 and the second substrate 112. A first transparent electrode layer 106 and a first alignment layer 108 are formed in that order on an inner surface of the first substrate 104, which faces toward the liquid crystal layer 118. A first polarizer 102 is formed on an outer surface of the first substrate 104, which faces away from the liquid crystal layer 118. A second transparent electrode layer 114 and a second alignment layer 116 are formed in order on a surface of the second substrate 112, which is near the liquid crystal layer 118. A second polarizer 110 is formed on an outer surface of the second substrate 112, which faces away from the liquid crystal layer 118.
The quality and performance of the alignment layers 108, 116 are key factors that determine the display quality of the liquid crystal display screen 100. A high quality liquid crystal display screens demand steady and uniform arrangement of liquid crystal molecules 1182 of the liquid crystal layer 118. This is achieved in part by correct arrangement of the liquid crystal molecules 1182 at the alignment layers 108, 116. Materials to make the alignment layers 108, 116 are typically selected from the group consisting of polystyrene, ramification of polystyrene, polyimide, polyvinyl alcohol, epoxy resin, polyamine resin, and polysiloxane. The selected materials is used to create a preform of each alignment layer 108, 116. The preform is then treated by one method selected from the group consisting of rubbing, incline evaporating oxide silicon, and atomic beam alignment micro-treatment. Therefore, grooves are formed on the treated surfaces of the preform, and the alignment layer 108, 116 obtained. The grooves affect the arrangement and orientations of the liquid crystal molecules 118.
In the liquid crystal display screen 100, the liquid crystal molecules 1182 are cigar-shaped. A plurality of parallel first grooves 1082 is formed at an inner surface of the first alignment layer 108. A plurality of parallel second grooves 1162 are formed on an inner surface of the second alignment layer 116. The first grooves 1082 are perpendicular to the second grooves 1162. The grooves 1082, 1162 function so as to align the orientation of the liquid crystal molecules 1182. In particular, the liquid crystal molecules 1182 adjacent to the alignment layers 108, 116 are aligned parallel to the grooves 1082, 1162 respectively. When the grooves 1082 and 1162 are at right angles and the substrates 104 and 112 are spaced appropriately, the liquid crystal molecules 1182 can automatically twist progressively over 90 degrees from the top of the liquid crystal layer to the bottom of the liquid crystal layer 118.
The alignment layers 108 and 116 can be made using a rubbing method. The rubbing method can be exemplified using the manufacturing method for the alignment layer 116. The manufacturing method for the alignment layers 116 generally includes the steps of: coating a layer of alignment material, such as polyimide, on the inner surface of the second transparent electrode layer 114; and rubbing the surface of the alignment material using rubbing cloth to form the plurality of fine grooves 1162.
However, some drawbacks arise from a mechanical contact of the rubbing cloth with the surface of the alignment material. This method is complicated because a baking process of the polyimide layer is very time-consuming, and the rubbing introduces large electrostatic charges as well as plenty of dust contamination, which in turn requires other facilities and cleansing processes to eliminate. In addition, the rubbing cloth has a limited lifespan and needs to be replaced frequently.
What is needed, therefore, is to provide a method for making a liquid crystal display screen with simple fabrication process.